1. Field of the Invention
The present invention relates to a laser annealing apparatus that irradiates an amorphous silicon film formed on a substrate with a plurality of laser beams through a plurality of microlenses to carry out a laser annealing treatment, and in particular, relates to a laser annealing apparatus and a laser annealing method, which facilitate maintenance and control of irradiation energy of the laser beams and enable suppression of shape disturbances in irradiation patterns.
2. Description of Related Art
Conventionally, this sort of laser annealing apparatus is one which forms a plurality of laser beams and forms a focal point for each beam by a microlens array, projects the focal point of each beam by a reduction optical system to form an image on an amorphous silicon film surface side, and thereby conducts a laser treatment by irradiation of the beams onto the amorphous silicon film surface, to change the amorphous silicon film in the thin-film transistor (hereinafter, referred to as “TFT”) forming area into polysilicon. On an underside of the reduction optical system, a quartz plate is provided as a protection member to prevent contaminants which spread during an annealing treatment from adhering to the optical system (for example, refer to Japanese Laid-Open (Kokai) Patent Application Publication No. 2004-311906).
Furthermore, as an optical system protection device for preventing such contaminants from adhering to the optical system, there is an apparatus for focusing a laser beam by a condenser lens onto an object to be processed to conduct a process, the apparatus has a film provided between a reel-in reel and a reel-out reel and transmitting a laser beam so that it can be moved between the condenser lens and the object to be processed (for example, refer to Japanese Laid-Open (Kokai) Patent Application Publication No. H07-100670).
In the laser annealing apparatus described in Japanese Laid-Open (Kokai) Patent Application Publication No. 2004-311906, since a quartz plate is employed as a protection member for preventing contaminants from adhering to the optical system, it is possible to form the surface of the quartz plate to be flat and no shape disturbance of irradiation pattern occurs. However, there is a problem that a contaminated quartz plate needs to be replaced every time after a certain duration of use, and such work is troublesome. Accordingly, there has been a problem that it is not possible to maintain high irradiation energy of the laser beams stably for long periods.
Furthermore, in the optical system protection device described in Japanese Laid-Open (Kokai) Patent Application Publication No. H07-100670, a film is provided between a condenser lens and an object to be processed so that the film can be moved, and accordingly, there is an advantage in that it is not necessary to replace the film every time after a certain period of use, and that the maintenance is easy. However, since a pair of rolls guiding the film are not disposed along both sides across the condenser lens, and since the distance between the pair of rolls is long, there is a problem that longitudinal wrinkles parallel to the moving direction tend to be formed in the film between the rolls when a back tension is applied to the film. Accordingly, when such an optical system protection device is applied to the laser annealing apparatus of Japanese Laid-Open (Kokai) Patent Application Publication No. 2004-311906, there is a problem that the longitudinal wrinkles cause disturbance of irradiation pattern of the laser beams radiated onto a substrate, to prevent formation of each TFT-forming area into a predetermined shape in the annealing treatment.